4.10's vs 3.73's

merc123 · Jul 19, 2005

Glad I could help skullmaster.
I chose 3.73's simply because I plan to supercharge.

Many also told me outside the forums that 4.10's would be too much gear as well.

I'm not disappointed.

Give Me TP · Jul 19, 2005

skullmaster427 said:
01 gt 5 spd

I think your transmission is a Tremec 3650 as well. I know the 3650 was used in the Bullitt, so I assume it was used in the GT as well. The stock tires on mine are the same as yours so the rpm numbers would be the same.

lover · Jul 19, 2005

Dingleweed said:
For those of you that are trying to decide what gears to get, and what difference it makes in the actual torque applied to your back tires... try this out for size.

So, I have been doing a little homework trying to figure out if I want to get 4.10s or 4.30s. One thing that I did to help me decide was to graph the actual torque to the wheels (dyno WTQ x gear ratio x diff. gear ratio) for a variety of different gears versus my car's speed.

For the dyno WTQ numbers I used this graph that I found for a stock 1999 Cobra (since I haven't dynoed my car...yet):

(I forget where I found this, but it seems kind of typical, and my car is sort of near stock... for now... )

I then mapped out the torque curve and input the data into a data processing program that I use. Once the data was acquired, I calculated the torque to the wheels (after gears, and differential ratios). For speed I used the info for the stock 245/45R17 tires.

Here's the chart for 3.90 differential gears:

and for 4.10 gears...

and for 4.30 gears...

and for 4.56 gears...

Since actual torque to the wheels is directly proportional to your acceleration, just think of the vertical axis as the kick in the pants that you feel for that gear at that particular speed.

As you can see, from a roll in second gear (say on the 4.10 graph) from anywhere between 20 and 50 mph, you have an extra 500 or so ft-lbs of torque to the back wheels! So, for 4.10 gears, second gear pretty much feels like second gear with 3.27s with a 100 or so shot of nitrous!

These graphs and data are rather useful for other things; for instance, thrust (forward force) is your torque to the wheels divided my the radius of your back tire. Since the stock 245/45R17 tires are close to a foot in radius (12.84") you can approximately think of the vertical axes as the forward thrust of your car. Then divide that number by your car's weight and you have your forward thrust in g's. (Of course this is all assuming that you don't break traction...) Also, where you see the curves for a given set of gears cross is your optimal shift point for maximum acceleration and 1/4 mile times.

My conclusions:
After playing around with the numbers, I am definitely going with 4.30 gears! With sticky tires, first gear will launch you out of the hole like a freaked out cat on carpet. Then for regular city driving on street tires, second and thrid gear would make it feel like I've got another 100 to 130 ft-lbs of torque to pin me back in the seat for sh1ts and giggles!

I had the "fun" of analyzing this data for my own info and gear decision, but I thought the info and graphs might be useful for the rest of the community.

Enjoy...

Double Wow...
I bet you sat up front in class didn't you? Hey, you want to do my taxes? Lol
I'm just kidding. That was a lot of useful info. there.

5spd GT · Jul 20, 2005

Getting gears shouldn't be based on just performance.

In response to the comment about 3,000 rpm at 90mph with 4:10's...you might want to check the tach. It is higher than that (rpm wise).

Bulldog Stang · Jul 20, 2005

I live in Texas. I had the .373's and blew them out at Fun Ford Weekend (FRPP) I have since replaced them with the .410 (FRPP) and LOVE THEM!!!!! I really noticed a Torque difference with the .410's and they pull hard as S**T coming out of 1st. And yes you do have to shift pretty quick, especially coming out of the hole. The .410's keep the 4.6L right in the power band for drag racing. You have to shift at about 5200 - 5300 rpms to keep it in te power band but you can definitely feel the .410's when you shift. A lot more than the .373's that I had. Hell, I had to buy new tires just to keep from smoking the Nitto Extremes that I had. I now have Nitto DR's.
As for the Highway driving. Yeah the Rpm's are a little higher, but it is not really an issue. I think that I am at 3000 rpm's at 90 mph. I used to get about 300 miles to a tank but I now get about 265 miles to a tank, so i did notice a drop in gas mileage. But if you dont care about mileage, then definately go with the .410's

Dingleweed · Jul 20, 2005

But, how much of that drop in milage is due to you more frequently flooriing it and enjoying your new surge in torque to the back tires?

tomustang · Jul 20, 2005

Good info. Even those this thread is 1 out of 436565624567108764350134503560148650560145610436510394561034516439564956105643513485734985349587439857134957435843953496543956934593925932459435428047560608365086504650461098650196509456097560457643056314095604395634591263405963405962314

Give Me TP · Jul 20, 2005

5spd GT said:
Getting gears shouldn't be based on just performance.

In response to the comment about 3,000 rpm at 90mph with 4:10's...you might want to check the tach. It is higher than that (rpm wise).

No, it's 3000 rpm at 90 mph on both the stock tach and on Predator datalogging. Odometer readings match milepost markers very closely, so the speedometer adjustment done by the Predator is also correct.

jstreet0204 · Jul 20, 2005

Give Me TP said:
No, it's 3000 rpm at 90 mph on both the stock tach and on Predator datalogging. Odometer readings match milepost markers very closely, so the speedometer adjustment done by the Predator is also correct.

Sorry man, but 90mph in 5th is around 3200 rpm. It shows that on my datalogs. If you are at 3000 with close to stock size tires you have 3.90 gears.

skullmaster427 · Jul 20, 2005

grrrr this gear thing man i am telling ya... its getting me already.. i just gonna keep on search i guess.. and as i see that 4.10s r a little too wild for my car... and 3.73 seens to be too close to stock.. i guess i will be going for 3.90s! rpm sounds okie for me well tops i would go for... and the only mods i have in my list are not much as hp... but more to makeing the car a little better as pulleys... alu. drive shaft next thing will be fly wheel... my clutch its getting there.... (dunno yet witch one to get... as all the cars i had b4 all gm used most the time centerforce any good price vs. quality? better than stock ...now i should have no problem as far as rebalancing the engine on changing for a lighter fly wheel ...

01 gt 5spd

jstreet0204 · Jul 20, 2005

skullmaster427 said:
grrrr this gear thing man i am telling ya... its getting me already.. i just gonna keep on search i guess.. and as i see that 4.10s r a little too wild for my car... and 3.73 seens to be too close to stock.. i guess i will be going for 3.90s! rpm sounds okie for me well tops i would go for... and the only mods i have in my list are not much as hp... but more to makeing the car a little better as pulleys... alu. drive shaft next thing will be fly wheel... my clutch its getting there.... (dunno yet witch one to get... as all the cars i had b4 all gm used most the time centerforce any good price vs. quality? better than stock ...now i should have no problem as far as rebalancing the engine on changing for a lighter fly wheel ...

01 gt 5spd

The people saying 4.10's are too wild, are usually the ones that don't have them. There was a guy on here a while back that got 4.10's and his wife didn't like them because she had to shift to often, so he switch back to 3.73's and regretted it. You might find 1 person in a 100 that doesn't like the 4.10's after they get them. You have to remember that alot of the impression that 4.10's are too much comes from back in the days when you could get them as a factory option on cars with no overdrive transmission.

Give Me TP · Jul 20, 2005

jstreet0204 said:
Sorry man, but 90mph in 5th is around 3200 rpm. It shows that on my datalogs. If you are at 3000 with close to stock size tires you have 3.90 gears.

Sorry, but they were a new in-the-box FRPP ring & pinion set (FRPP 8.8" gear sets do not come in 3.90), the drive shaft revolutions per complete turn of the rear wheel are correct, and I was present during the installation. I will, however, look closely at the tach again today if I can get up to 90 mph and report back here my error if it is indeed 3200 rpm. An extra 200 rpm would actually be a good thing to me, because I've occasionally thought "should I have gone with 4.30s?".

Dingleweed · Jul 20, 2005

jstreet0204 said:
The people saying 4.10's are too wild, are usually the ones that don't have them. There was a guy on here a while back that got 4.10's and his wife didn't like them because she had to shift to often, so he switch back to 3.73's and regretted it. You might find 1 person in a 100 that doesn't like the 4.10's after they get them. You have to remember that alot of the impression that 4.10's are too much comes from back in the days when you could get them as a factory option on cars with no overdrive transmission.

Yeah, you frequently read about people that get one gear (say 3.90s) then after a couple weeks the say they wish they had gotten a more aggressive gear (say 4.10s).

I can't recall reading about anyone who after driving with the gears for a while wishes that they had gone with a more conservative gear...

Dingleweed · Jul 20, 2005

Give Me TP said:
Sorry, but they were a new in-the-box FRPP ring & pinion set (FRPP 8.8" gear sets do not come in 3.90), the drive shaft revolutions per complete turn of the rear wheel are correct, and I was present during the installation. I will, however, look closely at the tach again today if I can get up to 90 mph and report back here my error if it is indeed 3200 rpm. An extra 200 rpm would actually be a good thing to me, because I've occasionally thought "should I have gone with 4.30s?".

Also, you've got an 03 Mach. You might have a different 5th gear ratio than the Tremac 3650... I dunno... but I bet someone does...

Give Me TP · Jul 20, 2005

It's a Tremec 3650 (maybe that's unfortunate)with a 5th gear ratio of 0.62. There is also a fifth gear ratio of 0.68 used in some models, possibly the GT? That would explain the difference.

5spd GT · Jul 20, 2005

You guys need to read more: Many think the gears are to harsh, especially those that go on the highway frequently.

It is more than 3,000 rpm at 90mph. That is a marketing ploy to sway people to get 4:10's.

Just remember getting these high gears isn't all about sotp feel and drag racing. Think longterm here - mileage, more engine rpm's and revs, clutch/tranny components.

To many times there is the "sotp" feel info and not what is actually does mechanically.

Give Me TP · Jul 20, 2005

I do highway driving all of the time, most times at speeds well below 90 mph. 4.10s work for me, and for lowering the engine revs, that's when fifth gear is used.

5spd GT · Jul 20, 2005

You still push half the rpm's capabilities at cruise in 5th when your at 90mph. That is just at cruise I personally don't like doing that to my internals/piston rings for long periods of time...the steeper the gear the more internally abused.

billfisher · Jul 20, 2005

the internals will be fine. you lose longevity, but if that's your goal, then buy a toyoya. numerical advantage is more than sotp. just try 0-100 with 2.73 against 4.56. me, i have used 3.73's with no overdrive and the 302 lasted for many years. drag racing twice a week, trips across the country. my next gear is 4.56. for what it is worth.

skullmaster427 · Jul 20, 2005

i'm with u guys ""5spd gt""and ""give me tp"" the main reason, its rpm and mpg not really how long my engine will last.. i know it will last atleast 100kand + easy and getting spanked everyday.. but hey i already have a weekend warrior and i dont need a bad gasser for a every day drive car... not with the miles that i do every day... some gears pulleys and drive shaft i should be fine ...i just dont want to drop more than 4/6 miles per gallon...that lol and i am almost placing my order for 3.90s gonna wait a little more and see how things so...working on my home made intake first!!! custon made gt scoop cold air... that will be sweet.. stock looking

4.10's vs 3.73's

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